Pine species such as Pinus radiata produce suitable timber, when dried, to allow high quality paint treatments for exterior uses, such as weatherboards, fascia and other wood cuts.
Pine timber which exhibits strong resinous features at or near the surface to be painted can lead to an undesirable reduction in the quality of the paint finish. Resinous features may take the form of broad latewood bands, resin pockets, local or widespread resinous areas, which are largely associated with tree growth stresses, such as drought, wind, or insect or other damage.
The weathering properties of painted resinous wood are generally poor because of features such as resin bleed, where wood resin may exude through the paint film to produce unsightly deposits on the surface; or resin show-through, where footprints of the wood resinous areas are apparent without any resin breakthrough the paint surface. Resin show-through is potentially more common, as it may occur in moderately resinous wood and may be evident within the first year or two after painting. In comparison, resin bleed is associated with extremely resinous wood.
At low magnifications, resin show-through is observed as micro-blistering, bubbling, or in severe cases a crocodile skin appearance, of the painted surface. Visually, it is observed as paint shade differences revealing the resinous areas. Generally the paint in the resinous areas appears bleached or washed out and these effects occur because of different light scattering effects associated with the comparatively uneven paint surfaces.
A major use of painted exterior wood is in house claddings, where remediation costs may be high for wood exhibiting resin show-through. Consequently the wood processing industry's response to the issue of resin show-through is to avoid processing resinous wood for paint grades. Thus a significant volume of wood deemed resinous, is downgraded to lower value end uses.
It is an object of the present invention to provide improved or alternative treatments that substantially reduce or eliminate resin show-through in wood, particularly in wood normally considered too resinous for paint grades.